Method for sterilizing contact lenses

ABSTRACT

Method and apparatus for sterilizing contact lenses wherein the lenses are moved in a circular orbit within a microwave oven through variations of energy levels in the microwave field in the oven, with the orbit of movement being spaced from the floor of the oven.

CROSS REFERENCE TO RELATED APPLICATION

This is a continuation-in-part of application Ser. No. 553,788, filedNov. 21, 1983, and entitled Apparatus for Exposure to Microwaves nowabandoned.

BACKGROUND OF THE INVENTION

Approximately ten to fifteen million people in the United States usedaily-wear soft contact lenses. The major problem with the wearing ofthese lenses is the possibility of corneal infection. This is primarilythe result of two factors, the inability of the patient to sterilize thelenses without damaging them, and the fact that a scratch on the cornea,which is extremely susceptible to becoming infected, will not hurt whencovered by a comfortable soft contact lens.

Of the three main types of contact lenses, daily-wear hard lenses,daily-wear soft lenses and extended-wear soft lenses, only thedaily-wear soft lenses present a major problem of infection. It is thewearers of these lenses that have a problem due to the lack of anadequate means of home sterilization. The present methods ofdisinfection of soft lenses have inherent problems. The chemical methodresults in almost all patients becoming allergic to the preservatives inthe solutions and, therefore, unable to use the disinfecting method. Theheat method requires a long term, often overnight, heating of the lensesin a solution. This requirement for a very demanding disinfectionprocedure results in poor patient compliance. Heat disinfection alsocauses damage to the lenses.

Another problem involving lens sterilization is that of sterilizingbandage lenses. A bandage lens is a high water content hydrophilicextended-wear soft contact lens. It is used to protect the cornea in avariety of situations such as protection following corneal surgery, andin various disease processes that prevent normal healing of the cornealepithelium, including poorly healing epithelial defects, cornealinjuries and ulcerations.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic side view of an apparatus constructed inaccordance with this invention positioned within a microwave oven whichis illustrated in dashed lines.

FIG. 2 is a top view of a container for a pair of contact lenses.

FIG. 3 is a plan view of the container with the top removed.

FIG. 4 is a sectional view taken along lines 4--4 of FIG. 3.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to the drawings in detail, and particularly FIG. 1, referencecharacter 10 generally designates an apparatus for sterilizing contactlenses in accordance with this invention, positioned within a microwaveoven 12 which is shown in dashed lines. The apparatus 10 comprises aturntable 14 positioned on the floor 16 of the microwave oven. Theturntable 14 may be of any suitable type, such as a spring driventurntable sold by Nordic Ware of Minneapolis, Minn., under the trademarkMicro-Go-Round. A pair of posts 18 and 20 are suitably secured to thetop of the turntable 14 and extend upwardly to a generally centrallocation within the microwave oven 12. A transverse support 22 issecured to the upper ends of the posts 18 and 20 to extend transverselyfrom the vertical axis of the turntable 14 in a generally horizontalplane. The transverse member 22 is formed of a material which istransparent to microwaves, as well known in the art. A pair ofhorizontally spaced guides 24 (only one of which is shown in FIG. 1) areprovided on the top of the transverse member 22 to slidingly receive arectangular container generally designated by the reference character 26therebetween, such that the container 26 will be maintained in anupright position and will be moved through the interior of the oven 12in a circular orbit oriented on a horizontal plane when the turntable 14is placed in operation. It should also be noted here that the materialof construction of the container 26 is such as to be transparent tomicrowaves and is preferably a plastic material for safe handling.

As shown in FIG. 2, the top 28 of the container 26 is secured to thebody of the container by suitable hinges 30, such that the top 28 may beraised and lowered, and a suitable clasp 32 is provided on the oppositeside of the top 28 for securing the top 28 in a closed position. Aplurality of apertures 34 are provided through the top 28 for allowingsteam to escape from the container 26 when the apparatus is placed inuse, as will be described further below. Also, a pair of largerapertures 36 are provided in opposite corners of the top 28 which permitthe introduction of saline into the container 28 as will also bedescribed. Finally, an L is preferably placed near one end 38 of the top28 and an R is preferably placed adjacent the opposite end 40 of the top28 to indicate to the user where his respective left and right lensesshould be placed in the container.

As shown in FIGS. 3 and 4, the sides 42 and bottom 44 of the container26 are preferably solid, and a divider wall 46 extends transverselyacross the container 26 to divide the container in to left and rightsections 48 and 50. A convex protrusion 52 is located or formed on thebottom of the continer in each of the left and right sections. Eachprotrusion 52 is made of a material transparent to microwaves and is ofa size to receive a contact lens thereon, such that the contact lenswill be maintained in basically its normal configuration during thesterilizing operation to be described below. It may also be noted thatthe enlarged apertures 36 in the top 28 of the container as illustratedin FIG. 2 are offset vertically from the respect protrusions 52.

OPERATION

Preparatory to sterilization, the lenses are removed from the eye,cleaned in the normal way between the fingers with cleaning solution toremove any protein debris. The cleaned lenses are then placed over theprotrusions 52; whereupon the top 28 of the container 26 is closed andthe container is placed between the guides 24 on the transverse supportmember 22 with the apparatus 10 located within the microwave oven 12.The door of the oven is closed, the oven is turned on and the turntable14 is placed in operation. Thus, the container 26 and the lenses thereinwill be moved in a circular orbit on a horizontal plane within the oven12, well above the bottom 16, whereby the lenses will be repetitivelysubjected to variations of energy levels (hot and cold spots) in themicrowave field until the lenses are sterilized.

During operation of the apparatus 10, the lenses will dehydrate, butsince the lenses are resting on the convex protrusions 52, each lenswill not fold over and touch itself. As the lenses dehydrate, the steamgenerated thereby is free to escape through the apertures 34 in the top28.

It should also be noted that a radar absorbent material (not shown) ispreferably placed within the microwave oven during the irradiation toact as a load so the microwave oven is not being operated "empty" whichcould severely damage the magnetron, or energy source, since theunabsorbed microwave energy would be reflected back to the magnetron.

Following irradiation, the container 28 is removed and the patientintroduces sterile saline through the apertures 36 before touching thelenses. Since the apertures 36 are vertically offset from theprotrusions 52, the saline will be directed onto the bottom of thecontainer and gradually envelope the lenses to ensure that no shockloads will be imposed on the lenses which may result in damage. Afterthe container 26 has been partially filled with the saline solutionabove the level of the lenses. After the lenses are fully hydrated thepatient opens the top 28, removes the lenses and places them in theeyes.

Aquaflex™ (tetrafilcon A) hydrophilic contact lenses manufactured by UCOOptics Inc. of Rochester, N.Y., have been sterilized by use of thepresent invention. Organisms that have been studied to this date forsterilization of the hydrophilic lenses and the time required forsterilization are as follows:

    ______________________________________    Organism       Type           Time to Kill    ______________________________________    Escherecia coli                   Gram negative  2-4 minutes                   bacterium    Staphyloccus aureus                   Gram positive  6-8 minutes                   bacterium    Streptococcus pneumoniae                   Gram positive  30-45 seconds                   bacterium    Proteus vulgaris                   Gram negative  1-2 minutes                   bacterium    Candida albicans                   Gram positive  2-4 minutes                   fungus    Aspergillus fumigatus                   Gram positive  2-4 minutes                   fungus    Pseudomonas aeuriginosa                   Gram negative  2-4 minutes                   bacterium    Bacillus cereus                   Gram positive  4-6 minutes                   spore forming                   bacterium    Serratia marcescens                   Gram negative  2-4 minutes                   bacterium    Herpesvirus type 1                   DNA virus      2-4 minutes    Parainfluenza virus                   Single stranded                                  1-2 minutes    type 3         RNA virus    Rhinovirus     Double stranded RNA                                  2-4 minutes                   virus    Adenovirus type 1                   Double stranded                                  2-4 minutes                   DNA virus    ______________________________________

Virus contaminated contact lens studies are shown in the followingTable.

                  TABLE 1    ______________________________________    Effects of Microwaves on Virus    Virus     Time of Exposure (minutes).sup.a    Contaminated              0         1         2       4 6 8                                               10    ______________________________________    Contact lens    Adeno 1   +++.sup.b ++        +       0 0 0                                               0    HSV-1     .sup. 1.2 × 10.sup.6c                        4.5 × 10.sup.3                                    3 × 10.sup.1                                          0 0 0                                               0    PI-3      1.5 × 10.sup.5                        2 × 10.sup.3                                  0       0 0 0                                               0    Rhinovirus                4 × 10.sup.5                        3 × 10.sup.2                                  1.5 × 10.sup.1                                          0 0 0                                               0    ______________________________________     .sup.a Virus contaminated contact lens were exposed to microwaves for 0 t     10 minutes.     .sup.b +++ = CPE seen in greater than 50% of the cell culture.     ++ = CPE seen in 10 to 50% of the cell culture.     + = CPE seen in less than 10% of the cell culture.     .sup.c Plaque forming units per ml.

Changes may be made in the combination and arrangement of parts orelements or steps and procedures without departing from the spirit andscope of the invention as defined in the following claims.

What is claimed is:
 1. A method of sterilizing a contact lens,comprising the steps of:placing the lens in a microwave oven having afloor; generating microwaves in the oven, and moving the lens in agenerally circular orbit within the oven in spaced relation from thefloor of the oven until the lens is sterilized.
 2. The method defined inclaim 1 wherein the steps of placing the lens in the microwave andmoving the lens in the circular orbit are characterized further toinclude the steps of:supporting the lens in a container which istransparent to microwaves; and moving the container in said circularorbit.
 3. The method defined in claim 1 wherein the lens is maintainedwith its convex side up while being moved in the circular orbit.
 4. Themethod defined in claim 1 wherein the circular orbit is on a horizontalplane.